We are pleased to introduce the collection, 2022 Retrospective: Colloidal Materials and Interfaces. This collection aims to showcase original research and review-based papers on the most exciting developments of the past couple of years. The work presented here highlights the broad diversity of research performed across the section, and aims to put a spotlight on the main areas of interest. All research presented here seeks to display strong advances in theory, experiment, and methodology with applications to compelling problems. Authors are encouraged to showcase their most recent discoveries and to kickstart scientific discourse around them.

Shanghai Jiao Tong University

Central South University

Frontiers in Materials

Colloidal Materials and Interfaces

2022 Retrospective: Colloidal Materials and Interfaces

Colloidal materials and interfaces, with their profound impact on a myriad of applications, have witnessed an unprecedented surge in research activities. The amalgamation of diverse research endeavors has illuminated the multifaceted nature of colloidal materials and interfaces, showcasing their pivotal role across various disciplines (<a href="#B3">Wu et al., 2020</a>; <a href="#B2">Liu et al., 2021</a>; <a href="#B1">Kim et al., 2023</a>). Here the Research Topic “2022 Retrospective: Colloidal Materials and Interfaces” has unveiled the forefront of scientific inquiry and innovation within the dynamic realm of colloidal science. One of the key strengths of this Research Topic lies in its ability to display the extensive diversity of research undertaken across the section.The Research Topic embarked on a journey through five distinct papers, demonstrating a wide range of applications, from enhanced drug delivery systems and innovative ophthalmic formulations to the profound implications of mineral surface charge in reservoir rock dynamics. Five subjects are included: (1) emerging the synthesis of NiO-ZnO and NiO-CuO nanocomposites as a promising avenue for photocatalytic degradation of pollutants, which opens avenues for sustainable solutions in environmental remediation, aligning with the ever-growing importance of eco-friendly technologies (<a href="https://doi.org/10.3389/fmats.2022.832439">Weldekirstos et al.</a>); (2) exploring the potential of oxybutynin-nanoemulgel for enhanced skin permeation, laying the foundation for future innovations in topical drug administration, fostering possibilities for enhanced patient compliance and therapeutic efficacy (<a href="https://doi.org/10.3389/fmats.2022.848629">Mohammadi-Samani et al.</a>); (3) delving into the intricate world of reservoir rock dynamics, emphasizing the role of mineral surface charge in wettability alteration, contributing to the efficiency of hydrocarbon extraction, and underscoring the significance of interdisciplinary approaches in solving real-world challenges <a href="https://doi.org/10.3389/fmats.2022.891455">(Mohammed et al.</a>); (4) comprehensively reviewing the unfolded the unique properties of nanocellulose from a colloidal material perspective, navigating through the colloidal intricacies of nanocellulose, shedding light on its unique properties that render it a material of choice in diverse applications (<a href="https://doi.org/10.3389/fmats.2023.1231404">Sanchez-Salvador et al.</a>); (5) presenting a breakthrough in ophthalmic drug delivery with the formulation and evaluation of microemulsions for enhanced topical administration of brinzolamide (<a href="https://doi.org/10.3389/fmats.2024.1363138">Zafar et al.</a>). These contributions collectively underline the interdisciplinary nature of colloidal science, where researchers seamlessly integrate principles from chemistry, physics, biology, and engineering to unravel the complexities of colloidal materials and interfaces.As we close this Research Topic, we extend our heartfelt appreciation to the authors, whose meticulous research has enriched our understanding of colloidal science. Additionally, we express gratitude to the reviewers for their invaluable contributions in ensuring the quality and rigor of the presented work. This Research Topic stands not only as a reflection on the past but also as a beacon guiding future exploration. The insights gained from these contributions will undoubtedly serve as a foundation for future breakthroughs, inspiring researchers to dig deeper into the details of colloidal materials and interfaces.We look forward to the continued evolution of colloid materials and interfaces, anticipating the next wave of discoveries that will shape our understanding of materials at the molecular and nanoscale levels. As we bid farewell to this Research Topic, we do so with a sense of anticipation, knowing that the journey of exploration and discovery is far from over.ZG: Writing&#x2013;original draft, Writing&#x2013;review and editing.The author declares that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.The author(s) declared that they were an editorial board member of Frontiers, at the time of submission. This had no impact on the peer review process and the final decision.All claims expressed in this article are solely those of the authors and do not necessarily represent those of their affiliated organizations, or those of the publisher, the editors and the reviewers. Any product that may be evaluated in this article, or claim that may be made by its manufacturer, is not guaranteed or endorsed by the publisher.

Editorial: 2022 Retrospective: colloidal materials and interfaces

Microemulsions (μEs) are more effective than conventional formulations for ophthalmic use due to their optical transparency, thermodynamic stability, structural flexibility and higher bioavailability. In addition, μE formulations can increase the water solubility of the drug and improve drug absorption in the eye. Herein, we report the development of three new biocompatible μE formulations containing an antihypertensive drug brinzolamide (BZD) and their evaluation for topical ocular administration. For this, Formulations A, B and C were optimized using an appropriate ratio of isopropyl myristate (IPM) as oil phase, water as aqueous phase and 2-propanol as co-surfactant, while Tween-80, Tween-20 and Tween-60 were selected as surfactant for each formulation, respectively. Preliminary, pseudoternary phase diagrams were delineated and then electrical conductivity and optical microscopy were used to establish optimal formulation for each μE to upheld the appropriate amount of BZD, i.e., 2.0 wt%, 2.0 wt%, and 1.0 wt% in formulation A, B and C, respectively. Dynamic light scattering demonstrated very fine monomodal assembly of BZD-μE nanodroplets (∼50 nm), while FTIR analysis showed effective encapsulation of BZD into hydrophobic microenvironment with no observable chemical interaction between BZD and μE excipients, which was further verified by the peak-to-peak concomitant measurement of fluorescence. Further, in-vitro release of BZD-μE showed enhanced and persistent topical ocular administration (>99%) within 10 h demonstrating the appropriate formulation for topical instillation.

Microemulsions (μEs) are more effective than conventional formulations for ophthalmic use due to their optical transparency, thermodynamic stability, structural flexibility and higher bioavailability. In addition, μE formulations can increase the water solubility of the drug and improve drug absorption in the eye. Herein, we report the development of three new biocompatible μE formulations containing an antihypertensive drug brinzolamide (BZD) and their evaluation for topical ocular administration. For this, Formulations A, B and C were optimized using an appropriate ratio of isopropyl myristate (IPM) as oil phase, water as aqueous phase and 2-propanol as co-surfactant, while Tween-80, Tween-20 and Tween-60 were selected as surfactant for each formulation, respectively. Preliminary, pseudoternary phase diagrams were delineated and then electrical conductivity and optical microscopy were used to establish optimal formulation for each μE to upheld the appropriate amount of BZD, i.e., 2.0 wt%, 2.0 wt%, and 1.0 wt% in formulation A, B and C, respectively. Dynamic light scattering demonstrated very fine monomodal assembly of BZD-μE nanodroplets (∼50 nm), while FTIR analysis showed effective encapsulation of BZD into hydrophobic microenvironment with no observable chemical interaction between BZD and μE excipients, which was further verified by the peak-to-peak concomitant measurement of fluorescence. Further, in-vitro release of BZD-μE showed enhanced and persistent topical ocular administration (&gt;99%) within 10 h demonstrating the appropriate formulation for topical instillation.

Formulation and evaluation of ophthalmic microemulsion for enhanced topical administration of brinzolamide

Cellulose nanomaterials present unique properties of interest for their many applications. Their behavior is mainly related to the colloidal properties that determine their self-assembly and stability mechanisms as well as their interaction with the particles present in different matrices. This review shows the state of the art of nanocellulose from a colloidal material perspective, from the approach of how to control these properties and their influence on the final products, such as drug delivery, coatings, nanocomposites, or tissue engineering, emphasizing the role of colloidal behavior in determining their performance.

Cellulose nanomaterials present unique properties of interest for their many applications. Their behavior is mainly related to the colloidal properties that determine their self-assembly and stability mechanisms as well as their interaction with the particles present in different matrices. This review shows the state of the art of nanocellulose from a colloidal material perspective, from the approach of how to control these properties and their influence on the final products, such as drug delivery, coatings, nanocomposites, or tissue engineering, emphasizing the role of colloidal behavior in determining their performance.

Nanocellulose from a colloidal material perspective

The reservoir rock ismade up of differentminerals which contribute to the overall formation wettability. These minerals in their natural state differ in chemistry and structure, and thus behave differently in an environment of varying composition and salinity. These have direct implications for enhanced oil recovery due to water flooding, or wettability alteration due to long-term exposure to brine. With the reservoir rock being a complex system of multiple minerals, the control of wettability alterations becomes difficult to manage. One of the dominant mechanisms responsible for wettability alteration is the mineral surface charge, which is dependent on pH, and fluid composition (salt type and salinity). For the first time, the surface charge development of barite, dolomite, and feldspar minerals in their native reservoir environments (accounting for the formation brine complexity) is presented. Also, the effect of oilfield operations (induced pH change) on minerals’ surface charge development is studied. This was achieved by using the zeta potential measurements. The zeta potential results show that barite and dolomite minerals possess positively charge surfaces in formation water and seawater, with feldspar having a near-zero surface charge. Furthermore, the surface charge development is controlled by the H+/OH− (pH), electrical double-layer effect, as well as ion adsorption on the mineral’s surfaces. These findings provide key insights into the role of fluid environment (pH, composition) and oilfield operations on mineral surface charge development. In addition, the results show that careful tuning of pH with seawater injection could serve as an operational strategy to control the mineral surface charge. This is important as negatively charged surfaces negate wettability alteration due to polar crude oil components. Also, the design of an ion-engineered fluid to control the surface charge of minerals was implemented, and the results show that reduction in the Ca2+ concentration holds the key to the surface charge modifications. Surface charge modifications as evidenced in this study play a critical role in the control of wettability alteration to enhance production.

The reservoir rock ismade up of differentminerals which contribute to the overall formation wettability. These minerals in their natural state differ in chemistry and structure, and thus behave differently in an environment of varying composition and salinity. These have direct implications for enhanced oil recovery due to water flooding, or wettability alteration due to long-term exposure to brine. With the reservoir rock being a complex system of multiple minerals, the control of wettability alterations becomes difficult to manage. One of the dominant mechanisms responsible for wettability alteration is the mineral surface charge, which is dependent on pH, and fluid composition (salt type and salinity). For the first time, the surface charge development of barite, dolomite, and feldspar minerals in their native reservoir environments (accounting for the formation brine complexity) is presented. Also, the effect of oilfield operations (induced pH change) on minerals’ surface charge development is studied. This was achieved by using the zeta potential measurements. The zeta potential results show that barite and dolomite minerals possess positively charge surfaces in formation water and seawater, with feldspar having a near-zero surface charge. Furthermore, the surface charge development is controlled by the H+/OH− (pH), electrical double-layer effect, as well as ion adsorption on the mineral’s surfaces. These findings provide key insights into the role of fluid environment (pH, composition) and oilfield operations on mineral surface charge development. In addition, the results show that careful tuning of pH with seawater injection could serve as an operational strategy to control the mineral surface charge. This is important as negatively charged surfaces negate wettability alteration due to polar crude oil components. Also, the design of an ion-engineered fluid to control the surface charge of minerals was implemented, and the results show that reduction in the Ca2+ concentration holds the key to the surface charge modifications. Surface charge modifications as evidenced in this study play a critical role in the control of wettability alteration to enhance production.

Investigation of Surface Charge at the Mineral/Brine Interface: Implications for Wettability Alteration

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The photocatalytic process over semiconducting oxide surfaces has attracted worldwide attention as a potentially efficient, environmentally friendly, and low-cost method for wastewater treatment. This study presents a straightforward, inexpensive, and rapid route for the synthesis of nickel oxide (NiO) and its composites with zinc oxide (NiO/ZnO) and copper oxide (NiO/CuO) nanoparticles through the chemical precipitation method using capping agent-hexadecyltrimethylammonium bromide (CTAB) for photocatalytic degradation of the methylene blue dye. The structure, morphology, and elemental constituents were characterized by X-ray diffraction, scanning electron microscopy, and energy-dispersive X-ray spectroscopy. The energy band gap of pure NiO, NiO-ZnO, and NiO-CuO composites was evaluated using the Tauc plot from absorption spectra and resulted as 3.00, 2.90, and 3.25&#xa0;eV, respectively. The optimum parameters for all photocatalysts were the following: pH 8, irradiation time 175&#xa0;min, catalyst amount 75&#xa0;mg, and dye concentration 7&#xa0;mg/L. At these optimum parameters, the degradation efficiency of the prepared photocatalysts toward the MB dye achieved was 89.8% for NiO, 97% for NiO/ZnO, and 94.2% for NiO/CuO. The highest activity of the p-type/n-type (NiO/ZnO) nanocomposite for MB degradation is possibly due to electron&#x2013;hole pair recombination inhibition by charge transfer processes. Therefore, semiconducting composite-based nanocatalysts such as NiO/ZnO with high photocatalytic activity are promising for future industrial applications to remove undesirable organic pollutants from the environment.

Surfactant-Assisted Synthesis of NiO-ZnO and NiO-CuO Nanocomposites for Enhanced Photocatalytic Degradation of Methylene Blue Under UV Light Irradiation

Among different topical drug delivery systems, nanoemulsions (NEs) are attractive due to enhanced skin permeation potential and minimum toxicity. Topical nanoemulgels (NEMGELs) contain both gelling agents and NEs and thus can enhance skin permeation with sustained effects at the site of application. Oxybutynin (OXB) is an anti-muscarinic agent that is administered orally to treat hyperhidrosis but its systemic side effects may decrease patient compliance. Therefore, it assumes that oxybutynin-nanoemulgel (OXB-NEMGEL) with sustained release properties and skin permeation ability may be a suitable alternative. Using Design Expert software®, 17 OXB-NE formulations were prepared and optimized based on particle size, zeta potential and physical stability. Three polymers were used to prepare and optimized OXB-NEMGEL based on spreadability and viscosity. In-vitro drug release and ex-vivo skin permeation were investigated for optimized formulation. The model suggested by Design-Expert was quadratic and there was significant association between response variables including particle size and zeta potential and independent variables (Oil:Surfactant ratio, Oil:Water ratio, and surfactants HLB) with P-values of 0.0334 and 0.0173, respectively. Also, the lack of fit was not significant (P-values 0.057 and 0.569, respectively) which confirms the fitness of this model. Average size and zeta potential of optimized nanoemulsions were 99 ± 0.1 nm and -57.3 ± 0.5 mv, respectively. Carboxymethyl cellulose-based nanoemulgels (CMC-NEMGEL) showed acceptable viscosity with a shear thinning rheological pattern and good spreadability which released OXB within 8 h. Ex-vivo OXB skin permeation revealed OXB flux of 1.5 ± 0.3 and 3.6 ± 0.2 μg/cm2/h after 12 and 24 h, respectively, which was equal to 5.3 ± 1.1% and 11.9 ± 0.7% of drug, while simple OXB gel did not permeate through skin layers. Thus, OXB-NEMGEL with effective skin permeation potential would be a novel promising drug delivery system for hyperhidrosis management which may lower systemic side effects.

Among different topical drug delivery systems, nanoemulsions (NEs) are attractive due to enhanced skin permeation potential and minimum toxicity. Topical nanoemulgels (NEMGELs) contain both gelling agents and NEs and thus can enhance skin permeation with sustained effects at the site of application. Oxybutynin (OXB) is an anti-muscarinic agent that is administered orally to treat hyperhidrosis but its systemic side effects may decrease patient compliance. Therefore, it assumes that oxybutynin-nanoemulgel (OXB-NEMGEL) with sustained release properties and skin permeation ability may be a suitable alternative. Using Design Expert software®, 17 OXB-NE formulations were prepared and optimized based on particle size, zeta potential and physical stability. Three polymers were used to prepare and optimized OXB-NEMGEL based on spreadability and viscosity. In-vitro drug release and ex-vivo skin permeation were investigated for optimized formulation. The model suggested by Design-Expert was quadratic and there was significant association between response variables including particle size and zeta potential and independent variables (Oil:Surfactant ratio, Oil:Water ratio, and surfactants HLB) with P-values of 0.0334 and 0.0173, respectively. Also, the lack of fit was not significant (P-values 0.057 and 0.569, respectively) which confirms the fitness of this model. Average size and zeta potential of optimized nanoemulsions were 99 ± 0.1&nbsp;nm and -57.3 ± 0.5 mv, respectively. Carboxymethyl cellulose-based nanoemulgels (CMC-NEMGEL) showed acceptable viscosity with a shear thinning rheological pattern and good spreadability which released OXB within 8&nbsp;h. Ex-vivo OXB skin permeation revealed OXB flux of 1.5 ± 0.3 and 3.6 ± 0.2&nbsp;μg/cm2/h after 12 and 24&nbsp;h, respectively, which was equal to 5.3 ± 1.1% and 11.9 ± 0.7% of drug, while simple OXB gel did not permeate through skin layers. Thus, OXB-NEMGEL with effective skin permeation potential would be a novel promising drug delivery system for hyperhidrosis management which may lower systemic side effects.